1. Technical Field
The present invention relates generally to an evaporative emission control system for an automotive vehicle and, more particularly, to a leak detection assembly and method for determining if a leak is present in a portion of an evaporative emission control system for an automotive vehicle.
2. Discussion
Modern, gasoline powered automotive vehicles typically include a fuel tank and an evaporative emission control system that collects fuel vapors generated in the fuel tank. The evaporative emission control system includes a vapor collection canister, usually containing an activated carbon, to collect and store fuel vapors. Normally, the canister collects fuel vapors which accumulate during refueling of the automotive vehicle or from increases in fuel temperature. The evaporative emission control system also includes a purge valve placed between an intake manifold of an engine for the automotive vehicle and the canister. The purge valve is opened by an engine control unit an amount determined by the engine control unit to purge the canister, i.e., the collected fuel vapors are drawn into the intake manifold from the canister for ultimate combustion within the engine.
Recently, governmental regulations have required that certain gasoline powered automotive vehicles have their evaporative emission control systems checked to determine if a leak exists in the system. As a result, on board vehicle diagnostic systems have been developed to determine if a leak is present in a portion of the evaporative emission control system. One such diagnostic method utilizes a vent valve to seal the canister vent, a sensor to monitor system pressure, and a purge valve to draw a vacuum on the evaporative emission control system. The method then monitors whether a loss of vacuum occurs within a specified period of time.
Diagnostic systems also exist for determining the presence of a leak in an evaporative emission control system which utilize positive pressurization rather than negative pressurization, i.e. a vacuum. In positive pressurization systems, the evaporative emission control system is pressurized to a set pressure, typically through the use of an air pump. A sensor determines whether a loss of pressure occurs over a certain amount of time. There are also pressurization systems which use various methods of sensing flow to determine if a leak is present.
While positive and negative pressurization systems have achieved success, there is room for improvement in the art. For instance, it would be desirable to provide a leak detection system which does not require either positive or negative pressurization from an outside source. Additionally, a leak detection system which functions when the vehicle is not operating avoids many of the complicating issues which makes leak detection on an operating vehicle a very difficult undertaking.